// Copyright 2011 The LevelDB-Go and Pebble Authors. All rights reserved. Use // of this source code is governed by a BSD-style license that can be found in // the LICENSE file. // Package crc implements the checksum algorithm used throughout pebble. // // The algorithm is CRC-32 with Castagnoli's polynomial, followed by a bit // rotation and an additional delta. The additional processing is to lessen the // probability of arbitrary key/value data coincidentally containing bytes that // look like a checksum. // // To calculate the uint32 checksum of some data: // // var u uint32 = crc.New(data).Value() // // In pebble, the uint32 value is then stored in little-endian format. package crc // import "github.com/cockroachdb/pebble/internal/crc" import "hash/crc32" var table = crc32.MakeTable(crc32.Castagnoli) // CRC is a small convenience wrapper for computing the CRC32 checksum used by // pebble. This is the same algorithm as used by RocksDB. type CRC uint32 // New returns the result of adding the bytes to the zero-value CRC. func New(b []byte) CRC { return CRC(0).Update(b) } // Update returns the result of adding the bytes to the CRC. func (c CRC) Update(b []byte) CRC { return CRC(crc32.Update(uint32(c), table, b)) } // Value returns the cooked CRC value. The additional processing is to lessen // the probability of arbitrary key/value data coincidentally containing bytes // that look like a checksum. func (c CRC) Value() uint32 { return uint32(c>>15|c<<17) + 0xa282ead8 }